Circuit interrupter



Feb 24, 1959 s. A. BOTTONARI 2,875,300

CIRCUIT INTERRUPTER Filed Deo. 9, 1955 4 Sheets-Sheet 1 wlTNessEsINVENTOR M Samuel A. Bof'ronorl.

ATTORNE Feb. 24, 1959 s. A. BOTTON'ARI CIRCUIT INTERRUPTER 4Sheets-Sheet 2 Filed Dec. 9, 1955 Isl NN mmm mNN Feb. 24, 1959 s. A.BoTToNARl 2,875,300

CIRCUIT INTERRUPTER Filed Deo. 9, 1955 4 Sheets-Sheet 5 Feb. 24, 1959 s.A. BOTTONARI CIRCUIT INTERRUFTER 4 Sheets-Sheet 4 Filed Deo.

United States Patent O CIRCUIT INTERRUPTER Samuel A. Bottonari,Pittsburgh, Pa., assigner to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Application December 9,1955, Serial No. 552,058 12 Claims. (Cl. 20o-146) This invention relatesto circuit interrupters and, more particularly, to high-speed circuitinterrupters.

Modern high-power direct current systems have many large rectiersoperating in parallel, and such systems are subject to a fault conditionparticular to mercury arc rectiiers known as arc back. This fault or arcback is caused by the occasional inability of an anode and cathode pairto withstand the inverse voltage oc curring during the normallynon-conducting portion of the cycle. Reverse or back current then beginsand, once started, it increases rapidly. The ultimate current is limitedby the arc drop of the faulted anodecathode pair, by the resistance ofthe reverse current path, and by the regulation of the remainder of thedirect current system. Since the direct current system is large, andresistances in the reverse current path are low, the ultimate current isrelatively large.

The ultimate arc-back current is much greater than that which might betolerated, even momentarily, by the rectifier equipment due to themechanical stresses and overheating involved. A cathode circuitinterrupter, when used for arc-back protection must, therefore, openfast enough to limit the current to a tolerable value. In order to startthe limitation of fast rising fault currents the earliest possiblecontact separation is required, and maximum contact opening accelerationis required to obtain early are lengthening and to withstand the highvoltage across the contacts during and after interruption.

In conventional circuit interrupters, the amount of time` available forsequential separation of the main and arcing contacts does not present aditiicult problem. However, in high-speed circuit interrupters involvingopening operations within l cycle, based on 60 cycle A. C. current, theproblem of reducing the opening time to a minimum, yet have time tofirst separate the main contacts and then separatethe arcing contacts,becomes a very diflicult problem. The time used in separating the maincontacts is wasted, yet conventional circuit interrupters rely oncontact iiexibility to make sure that Contact pressure is maintainedthrough the small movement of main contact follow. I have found that byincreasing the main contact mass the contact follow of the mainstationary contact is slowed up. Even though satisfactory contactpressure is assured by spring pressure, the spring force need not besufficient to instantly move the large mass of the main stationarycontact if the movable contact structure is tripped and moved to openposition at high speed. Thus by using such an arrangement together witha movable arcing contact having a small mass and a high opening force,this contact separation time is limited essentially to the time it takesthe arcing contacts to separate.

An object of this invention is to provide a circuit interrupterembodying a contact structure capable of high-speed opening operation.

Another object of the invention is to provide a circuit interrupterembodying a contact structure capable of ICS early Contact separationfollowing a tripping operation and high acceleration in openingdirection.

Another object of the invention is to provide a circuit interrupter'embodying an improved contact structure in which the main stationarycontact is movable a small amount and biased to provide contactpressure, the ratio of the mass of the main contact to the force of thebiasing means being relatively high to make the main stationary contactdynamically slow in motion.

Another object of the invention is to provide a circuit interrupterembodying an improved contact structure according to the precedingparagraph in which the ratio of the mass of the moving arcing contact tothe force of the accelerating spring is relatively low to provide earlyseparation of the main contacts and high-speed opening of the contacts.

The invention, both as to structure and operation together withadditional objects and advantages thereof, will be best understood fromthe following detailed description thereof when read in conjunction withthe accompanying drawings.

ln said drawings:

Figure 1 is a side elevational view partly in section of a circuitinterrupter embodying the principles of the invention;

Fig. 2 is an enlarged elevational view of the stationary contactstructure;

Fig. 3 is a horizontal sectional view taken on line III-III of Fig. 2and looking in the direction of the arrows;

Fig. 4 is an enlarged elevational view of the movable contact structure;

lFig. 5 is a sectional view taken on line V-V of Fig. 4 and looking inthe direction of the arrows;

Fig. 6 is an elevational view of a modified form of the contactstructure; and

Fig. 7 is a top plan View of the contact structure shown in Fig. 6.

Referring to Fig. 1 of the drawings, the circuit interrupter is mountedin a rigid metal frame comprising a base portion 11 having spacedupright frame members 13 of insulating material rigidly secured to thebase portion 11 at one end and similar but shorter spaced upright framemembers 15 also of insulating material rigidly secured to the baseportion 11 at the opposite end thereof. The circuit interrupter alsoincludes stationary contact means indicated generally at 17 (Figs. 1 and2) and movable contact means indicated generally at 19, operatingmechanism indicated at 21, and a trip device shown generally at 23.

The stationary contact means comprises an arcing contact member 2S (Fig.2) secured by means of bolts 27 to the upturned end 29 of a conductingbar 31. The conducting bar 31 is rigidly supported by means of aU-shaped bracket 33 (Figs. 2 and 3), the side portions 35 of which arerigidly mounted between the spaced frame members 13 by means of bolts37. The lefthand end of the conducting bar 31 is secured by means ofbolts 39 to a horizontal portion 41 of the bracket 33. The other end ofthe conducting bar 31 is rigidly supported by a support bar 43 havingone end secured to the conducting bar 31 by means of bolts 45 (only onebeing shown) and the other end rigidly secured by means of bolts 47(only one being shown) to the bracket 33 adjacent the upper end thereof.A pair of main stationary contact bars 49 (Figs. 2 and 3) each having acontact member 51 rigidly secured to the right-hand end thereof aresupported beneath the conducting bar 31 for limited movement or Contactfollow relative thereto. The contact bars 49 are supported on a supportplate 53 which is rigidly supported on the conducting bar 31 by means ofpairs of side plates 55 and 57, the side plates beingsecured to the'conducting bar 31 and to the support plate 53 by meansA of screws 59.Ther rightf pin 63 in the support plate 53 adjacent the right-hand endthereof. The left-hand end of the bars 49 are slidably supported on thesupport plate 53.

The main contact bars 49 have passages'therein to circulate-a suitablefluid for cooling purposes. The contact barsl 49 have integral laterallyextending projections 65, each of which is provided with a connection 67for connecting the contact bars'to a sourceV of fluid. Thecontact bars459 also are provided with pipes 69 for' completingA the circuit of thecooling Huid.

The contactv bars 49 are biased toward the right (Figs.V 2 and 3) bycoil springs '71 coiled around the pipes 69 and compressed between theYcontact bars 49 and an angular bracket 73, the upturned left end ofwhich is rigidly vsecured by means ofV bolts 75v to a bar 77. The

bar 77 is welded or otherwise rigidly secured to the outer' end oftheportion 41 of ithe bracket 33 and to a center ribV 79 of the bracket 33.As seenin Fig. 3, ther'side portions 81 of the bracket 73 have formedover portions 83 which engage the top surfaceV of the conducting bar 31to rigidly support the bracket 73.

Each of the contact bars 49 is connected by means of flexible conductorsS4and S6 to conducting ,blocks 88 mounted'on the conducting bar 31 bymeans of'bolts 90, the exible conductors 34, 86 being secured by meansof bolts 92 toV the vprojections 65* of the contact bars 49 and by meansofbolts 94 to the blocks 88., The movement of the main stationarycontact bars 49 is limited to a small amount by adjustable stop screwsSi) (Figs. 2 and 3) which are threaded into the left-hand ends of thecontact bars 49- andV locked in adjusted position by lock nuts (notshown). During an openingoperation, the ends of the stop screws St?engage the left end of the support plate 53 to limit thecontact follow.

The movable contact structure 19 (Fig. 4) comprises a main movingcontact S which cooperates with the main stationaryl contact member 51and a moving arcing contact 87 which cooperates with the stationaryarcing contact 25. The main moving contact 85 is rigidly mounted on theupper end oa Contact bar 89 rigidly securedby means'of bolts 91 and 93to a'channel-shaped contact'carrier 95. The side portions of thechannelshapedcontactcarrier 95 are individually pivotally supported-attheir'lower ends on spaced bars 97 and 99- by means ofspacedfpivots161', only oneof which is shown. The bars 97 and 99 are rigidlysecured'to the upright' frame`- members 13 and 15 and are joined bycross'mernbers'103'and15. Thesmoving arcing contact 87 is mounted bymeans of a bolt 107 on the'upper end of a `channel-shaped contact arm'1119 which is pivoted on'apinlll carried'by the side portions of thechannelshaped` carrier 95;

89 by a fiexible conductor 113v having its'upper'end secured between thearcing contact 87 and thel contact arm 109 by the bolt 107 and its lowerend secured to the contact bar S9 by means of a bolt 115. The arcing.

contact arm 169 is biasedin a counterclockwise direction b'y a spring`117 surrounding the bolt 91 and compressed between the contact bar 89and a spring seat 119 welded or. otherwiserrigidly secured to thesideportions ofthe arcing contact arm 109. A nut 121 threaded onto theright endof the bolt 91 serves as a stopfor the arcingv contact: arm109inthe open position of,themovable contact structure. The spring 117provides contact pres-- the uppery ends of a pair of flexibleconductors123 toi thelower end ofthe movable contact bar-.89. ThelowerThe movable arcing contact87 is connected'to theupper'end of the movablecontact barv ends of the exible conductors 123 are secured by means ofa'bolt 125 to a'vconductor 127 which is, in turn, secured to a mainconductor 129.

The movable contact structure 19 is biased in opening direction by meansof a strong spring 131 (Fig. 1') compressed between a retainer 133 heldon a spring rod 135 by means of a nut 137 threaded on one end of the rodand a ange 139 of a shock absorber 141. The other end of the rod 135 isconnected to-thepivot pin 111 (Figs. 4 and 5) on the movable contactstructure. The shock absorber 141- is mounted ina block 143 forming partof a bracket 145 which is secured to the bars 97 and 99. The arcing andmain contacts are closely coupled to reduce-the difference between theinductance of Vthe circuit paths through these contacts. t

The movable contact structure is held in the closed position against thebias of the accelerating spring 131 (Fig. l) by means of the trip device23 which includes aholding'magnet 147. The'holding magnetcomprises apair of armatures 149 and 151 connectedV to opposite endsofa bar 153' bylinks 155; A link 157 is pivotally connected at its lower end to themid-portion of the barl 153 andat its upper end is pivotally connectedby a pivot pin 159 to onefend of a rod 161 which has its other endpivotally connected by the'pin 111 to the mov-y ing contact carrier 95.One end of a link 163 ispivotallyV connected to theV link-157 and therod 161 by thepivot pin 159, and the other end of the link 163 isconnectedby means of a pivot pin- 165 to a lever 167 which has its otherend-pivoted on a fixed pivot 169. OneV endof a toggle link 171is-pivotally connectedto the link 163 and lever 167' by the pivot pin165, and the other endl ofl the. toggle link 171 is connected'by a kneepivot-pinV 1734 to. a: toggle link 175 lmounted on'a fixedpivot 177. Inthe closed position of the circuit interrupter with thearmatures 149 and151 in their attracted positions,

Va component-of thevforce of the-accelerating spring 131 holds.'thetogglell, 1.75 in an overset position against a. fixed stop 179Vand above a line drawn through the centers offthe pivots 165 and 177,thus maintaining the movable contact structure in the closedcontactpositionragainstthe force. of a spring 181which tends to causecollapse-of theigtoggle 171, 175. When either of the armatures 149 or151 is releasedby the holding magnet v147, thelink 157 andthe rod 161are free to move inV Whenthe toggle 171, 175A collapses, a pin 183 onthe` end of the toggle link Y175 opposite the. knee pin 173 movesyupwardly inan elongated slot 135 in a linl r1t7`whichV atits lower endis connected by, means ofa pin129:toy

a crank arm191. Collapse` of the toggle 171, 175 also effects vmovementof the released armatures 149er y151 to its attracted position where itis heldA upon correctionl of the abnormal circuit conditions whichleffected. itsL release. With both of the armatures 149, 151 held intheirattracted positionsby the .holding magnet, rotation oi?A the crankarm191. draws the link 187 downduring whichY movement 1 the upper end'.of' the slot 185 engages the pin 183. and resets the. toggle 171, 175Vtov its. overset position and, at the same time, acting.

through the link 163.and the rod ,161 moves the movable contactstructure to the closed Contact position.

The: holding4 magnet is of the typev disclosed and claimed: in copendingapplication Serial No. 507,595,

filed May 1l, 1955, by Joseph D. Findley and assigned to the'assignee ofthe instant application. For this reason onlya brief description oftheholding magnet will be' given. v

The holding magnet'comprises a U-shaped magnet yoke 193andthree-vpolepieces .195` whichbetween themctorm:

two air gaps, one associated with each of the armatures 149 and 151. Apair of coils 197 are mounted on the legs of the U-shaped magnet yoke193 to produce a magnetic ux that traverses the air gaps adjacent thearmatures 149 and 151. The coils 197 are connected to a suitable sourceof electrical energy.

The main current path adjacent the holding magnet comprisess-ubstantially parallel main conductors 199 and 201 which are connectedat one end to a terminal 203 and at their other ends to the conductor127 which is connected to the moving contact structure. The current paththrough the interrupter extends from the terminal 203, the parallelconductors 199 and 201, the conductor 127, movable and stationarycontact structures 19 and 17, axible conductors 84 and 86 to theconducting blocks 88 thence through a copper coolant pipe 205 (shownbroken away for clearness) to a terminal 207. Associated with the mainconductor 199 is a forward ux diverter 209 and a reverse ux diverter 211is associated with the parallel main conductor 201.

With the holding coils 197 energized and normal current owing in theparallel conductors 199 and 201, the armatures 149 and 151 are bothmaintained in their attracted positions, thus holding the movablecontact structure in the closed contact position. Upon a predeterminedrise of current in a forward direction, the current in the mainconductor 199 causes the ux to be shunted through the diverter 209around the air gap for the armature 149, thus reducing the ux throughthis armature to approximately zero causing high-speed release of thearmature and opening of the interrupter contacts.

When the direction of current ilow is reversed, the main conductor 201causes the magnetic ux to be shunted through the diverter 211 around theair gap for the armature 151 reducing the magnetic flux through thisarmature to approximately zero and causing high-speed release of thearmature 151 and opening of the contacts. The mechanism is reset and thecontacts closed following an opening operation in the previouslydescribed manner.

In order to obtain main contact separation as early as possible in theopening operation the ratio of the mass of the moving stationary contactbars 49 in pounds to the force of the springs 71 in pounds is relativelylarge compared to previous circuit interrupters. For example, this ratiomay be in the neighborhood of 1 to 10, which makes the contact barsdynamically slow. In one practical` form of the invention, the maincontact bars 49, for instance, may each weigh 7.5 pounds and the springs71 each may apply a force of 75 pounds. Also, the ratio of the mass ofthe movable contact structure to the force of the accelerating spring131 is relatively small, for example, of the order of l to 200, toprovide for highspeed separation of the contacts. The spring 117provides contact pressure and ensures that the movable arcing contact 87will separate after the main contacts separate and, in this action, thespring is assisted by the inertia of a mass of the movable arcingcontact which tends to remain stationary during the opening movementuntil the moving contact arm 109 engages the nut 121. It will thus beseen that the inertia of the movable portion of the stationary maincontacts permits the main contacts to separate quickly, for example, inless than .001 second, and the inertia of the movable arcing contactdelays separation of the arcing contacts, the total contact separationtime being, for example, napproximately .002 second.

In the modification of the contact structure shown in Figs. 6 and 7, themain stationary contact, in addition to the ratio of the mass to theactuating spring pressure, utilizes a gripping action caused by the fluxdue to parallel current paths through the contact member to furtherrestrain the action of instant motion or contact follow of the movableportion of the main stationary contact.

The stationary contact structure shown in Fig. 6 comprises generanl amain stationary contact member 215 slidably mounted on a conducting bar217, and a stationary arcing contact 219 rigidly secured by means of abolt V221 to the conducting bar 217. The conducting bar 217 is rigidlysupported in the same manner as the bar 31 as shown in Fig. 2. Thestationary main contact member 215 is U-shaped and is divided into aplurality of resilient fingers 223 which slidably engage the upper andlower surfaces of the conducting bar 217. A contact 225 is mounted onthe main contact member 215 and the contact member is biased by means ofone or more springs 227 into engagement with a plurality of movable maincontacts 229 which are individual contact ngers 231. The contact ngers231 are rigidly mounted by suitable means in a movable channel-shapedswitch arm 233 pivotally supported at its lower end on the bars 97, 99(Fig. 1) 'by means of spaced pivots not shown in Fig. 6 but which arelike the pivots 101 shown in Fig. 1. A movable arcing contact 235 ispivotally mounted on a pin 237 supported in the side members 239 of thechannel-shaped switch arm 233 and is biased by a spring 241 intoengagement with the stationary arcing con tact 219. The spring 241 iscompressed between a spring seat 243 on the movable arcing contact 235and an extension 245 of the switch member 233 and surrounds a rod 247threaded into the movable arcing contact. The rod 247 extends through aclearance opening in the extension 245 and has a nut 249 threaded ontothe outer end thereof which acts as a stop to limit the movement of themovable arcing contact 235 relative to the movable main contacts duringan opening operation. The spring rod and the operating rod 161 arepivotally connected to the pin 237 in order to operate the movableswitch arm 233 in the manner previously described.

The operation of the contact structure shown in Figs. 6 and 7 is similarto that of the contacts shown in Figs. l and 4. When either of thearmatures 149 or 151 (Fig. l) is released in response to a rise inforward or reverse current, the accelerating spring 131 snaps themovable switch arm 233 (Fig. 6) to the openposition at high speed. Dueto the relatively high ratio of the mass of the contact member 215 tothe force of the springs 227 the main stationary contact member 215tends to remain stationary while the moving main contact separatestherefrom very early in the opening movement. This action is aided Abythe parallel currents owing in the fingers 223 of the main stationarycontact member 215 which causes the ngers to apply a gripping force tothe support bar 217 and further delays or retards the movement orcontact follow of the contact member 215. The contact follow of the mainstationary contact member 215 is limited by engagement of shoulders 251(Fig. 7) on the inner ngers 223 engaging the inner end 253 of thestationary arcing contact 219.

The spring 241 ensures that the arcing contacts will separate after themain contacts separate and the spring 241 is aided by the inertia of themass of the moving arcing contact 235 which tends to remain stationaryduring the opening movement. It will thus be seen that inertia plus thegripping action caused by the parallel circuits in the ngers of the mainstationary contact member allows the main contacts to separate quiteearly in the opening operation, for example, in less than .001 second,and inertia assists the arcing contacts to remain in engagement untilafter the main contacts have separated a predetermined distance.

The current path between the main contacts and the current path betweenthe arcing contacts are closely and mutually coupled to reduce thereluctance between the current paths in order to keep the sparkingvoltage developed as a result of transferring the current from the maincontacts to the arcing contacts as low as possible to prevent pitting ofthe contacts and to avoid the use` of tlexible conductors.

Having described the. invention' in accordance with. the yprovisionsofthe patent statutes, it is tobeunderstood 'means having a relativelylargemass, stationary arcing contact means, meanssupportingfsaidstationary main. contact means for limited movement relativeto saidvstationary arcingcontact means, movable main and arcing contact means icooperating with said stationary main and arcing contact means, biasingmeans vbiasing. said stationary main. contact With-a relatively lightforce to providecontactpressure, operating means for moving saidmovablecontact means to open and closed positions, and the ratio of themass of said stationary main contact meanszto the forceof said. biasingmeans being relatively largey to make said. stationary maincontactdynamically slow inmotion and/thereby eiect separation of saidmain contact means Jearly, in'` anopening operation.

. 2. InV a circuit interruptor, stationary. main contact means-having arelatively. large mass, stationary arcing contact means,rmeanssupportingsaid stationary main contact means on said stationary arcingcontact means for limited sliding. movement relative tosaidstationaryarcing contact means, movable main andarcing contact means-cooperatingwith said stationary-main andarcingl contact means, biasing Vmeansbiasing said stationary main contact with a relatively light. force toprovide-.contact pressure, operating. means for moving said movablecontact means to open. and closed positions,.and the ratio ofthe mass.of .said stationary main contact means to therforce ofsaid biasingmeansbeing relatively large to make said stationary main contact dynamicallyslow inY motion and therebyeffectseparation of said main contactrneansearly in .an opening operation.

3. in a circuit interrupter, a stationaryy main contact having arelatively large mass, a stationary arcing contact, means supportingsaidstationary main contact 'for limited movementrelative to saidstationary arcing contact, a movable.. switch arm. having av movablemain contact rigidly mounted thereon,. a movable arcing Contactmounte'don. said switch arm for limitedmovement rela# tive to saidmovable main contact, biasing means biasing said stationary main Contactwith a relatively light force to provide contact pressure between'saidmain contacts,

means biasing said movable. arcing contact'to provide contact pressure,operating means biased to move saltiV movable switch arm to openposition to provide highspeed lopening of said contacts, the ratio ofthe mass of saidstationary main contact to the force o'itsbiasingmeans-being relatively large to make said stationary main contactdynamically slow in motion to thereby eiect early separation of saidmain contacts, and the mass of said...1:novable arcing contactassisting' its biasing means to maintainlsaid arcing contacts closeduntil after the main contacts have separated during an Vopeningoperation.

4. In a circuit interruptor, stationary main contact means having arelatively large mass, stationary arcing contactrneans, means supportingsaid stationary main.

contact means for limited movement relative to said stationary arcingcontact means, movable main and arcing ,contact means cooperating withsaid .stationary main and arcing contact means, the current pathsthrough. said main contacts and said arcing. contacts being closely andVmutually` coupled to reduce. the inductance of said current paths,biasing meansbiasing said stationary main contact with a relatively`light force toprovide contact pressure, operating means formovingvsaidmovable contact .means to open. and; closed positions, ,and theratio.ofrthe .mass of saidstationary main Acontact means :tothe w force. ofsaid biasingv means being relatively large to.

make said'l stationary main contact. dynamically. slow inmotion andthereby electseparation of said main.l contact means early in an.opening operation.

5. In. acircuit .interrupten relatively movable contactmeanscomprisingaa stationary arcing Contact, support means .rigidlysupporting said stationary arcing. Contact, a U-shaped stationary maincontact` member slidably supported von. saidsupport'means for limitedmovement relativeto .said .stationary arcing contact, the legsof saidU-shaped main contact member applying a pressure to opposite. sides ofsaid support means, movable. contact means comprising movable arcing andmain contacts cooperating With said stationary arcing and main contacts,operating means for moving said'movable contact means toppen and closedpositions, means biasing said- U-shaped stationary contact with .arelatively light force to provide contact pressure, andthe ratio of themass of said- U-shaped'i stationary main contact to the biasing force ofsaidf biasing means being relatively large to make' said stationary main.contact dynamically slow in motion.

6. In a circuit interrupter, relatively movablecontact means. comprisinga stationary arcing contact, support4 means rigidlyy supporting saidstationary arcing contact, a U-sliaped main stationary contact memberhaving legs engaging opposite sides of said support means slidablysupporting said main contact member on said support means for limitedmovement relative to said stationary arcing contact, the legs of saidU-shaped'stationary contact member forming parallel current paths,saidlegs. of said stationary 'main contact member applying.apredetermined pressure to opposite sides of said support means toretard movement of'said stationary main contact member, cooperatingmovable Contact means comprising movable arcing and main contacts,operating means for moving said'movable contact means to open and closedpositions, biasingrneans biasing said U-shaped main contact member toprovide contact pressure, and the legs of said U-sh'apedstationary Vmaincontact memb'erbeing responsive to the' current tlowing in saidparallelcurrent paths to increase the pressure of Vsaid legs .on said"support'member to further retardmovement of said U- shaped stationarymainfc'ontact member.

7`. In a circuit interrupter, relatively movable contact meanscomprising a stationary arcing contact, support means rigidly supportingsaid stationary arcing contact, a U-snaped main stationary contactmember having legs engaging opposite sides of saidsupportmeans slidablysupporting said'rnain contact member on said support means for limitedmovement'relative to saidvv stationary arcing contact, the legsof saidU-sbaped stationary 'con'- tact member forming parallelcurrentpaths,said legs'of` said'stationary main contact member applying apredetermined pressure to opposite sides of said support meansl toretard movement of saidstationary main contact member, cooperatingmovable contact means comprising movable arcing and main contacts,operating means for'moving. saidmovable:contactmeanstoopen and closedposi'-` ti'ons, biasing meansbiasingsaid'U-sliaped` main contactmemberto providecontact'pressure, the ratio of the mass of'saidstationary main contact member to the biasing force of said biasingmeans being'relatively` large to make* said stationary main contactmember dynamically slow in motion, andl the legs ofsaid U-shapedstationary main contactmember being responsive to the current owing in'said parallel current paths to'increase the pressure of saidV legs onsaid support member to Vfurther retard movement of saidl U-shaped"stationary main Contact member.'

S. In a circuit interrupter, relatively movable contact means comprisinga stationary arcing contact, support means rigidly supportingsaid'stationary arcing Contact, a

. stationary main Contact member slidablymountedon said support memberforlirnited movement relative to said' stationary,farcinggcontact, aplurality of resilient membersk members forming parallel current movablecontact means comprising movable arcing and main contacts, operatingmeans for moving said movable contact means to open and closedpositions, biasing means biasing said stationary main contact to providecontact pressure, and said resilient members being responsive to thecurrent flowing in said parallel current paths to increase the pressureof said resilient members on said support means to thereby furtherretard the movement of said stationary main contact member.

9. In a circuit interrupter, stationary main contact means having arelatively large mass, stationary arcing contact means, means supportingsaid stationary arcing contact means and supporting iXedly saidstationary main contact means for movement relative to said stationaryarcing contact means, stop means for limiting the movement of saidstationary main contact means, movable main and arcing contact meanscooperating with said stationary main and arcing contact means, biasingmeans biasing said stationary main contact means to provide contactpressure, operating means for etecting high-speed opening movement ofsaid movable contact means, the mass of said stationary main contactmeans and the force applied thereto by said biasing means being suchthat said main contacts separate before any substantial movement of saidstationary main contact means.

l0. In a circuit interrupter, stationary main contact means having arelatively large mass, stationary arcing contact means, means supportingsaid stationary main contact means for movement relative to saidstationary arcing contact means, stop means for limiting the movement ofsaid stationary main contact means, movable main and arcing contactmeans cooperating with said stationary main and arcing contact means,biasing means biasing said stationary main contact means to providecontact pressure, operating means for effecting high-speed openingmovement of said movable contact means, the mass of said stationary maincontact means and the force applied thereto by said biasing means beingsuch that paths, cooperating 10 said main contact means separate earlyin the movement of said stationary main contact and before the limit ofthe stationary main contact movement is reached.

1l. In a circuit interrupter, stationary main contact means having arelatively large mass, stationary arcing contact means, means supportingsaid stationary contact means for limited contact follow, movable mainand arcing contact means cooperating with said stationary main andarcing contact means, biasing means biasing said stationary main contactmeans to provide contact pressure, operating means for effectinghigh-speed opening movement of said movable contact means, and the ratioof the mass of said stationary mass contact means to the force of saidbiasing means being such that said main contact means separate early inthe stationary main contact follow and before the limit of said mainContact follow is reached.

l2. In a circuit intelrupter, stationary main contact means having arelatively large mass, stationary arcing contact means, means supportingsaid stationary contact means for limited contact follow, stop meanslimiting said main contact follow, movable main and arcing contact meanscooperating with said stationary main and arcing contact means, biasingmeans biasing said stationary main contact means to provide contactpressure, operating means for effecting high-speed opening movement ofsaid movable contact means, and the ratio of the mass of said stationarymass contact means to the force of said biasing means being such thatsaid main contact means separate early in said stationary main contactfollow and before the limit of said main contact follow is reached.

References Cited in the tile of this patent UNITED STATES PATENTS2,069,641 Bold et al. Feb. 2, 1937 2,214,471 Ludwig et al Sept. 10, 19402,545,341 Caswell Mar. 13, 1951 2,691,086 Milne et al. Oct. 5, 1954

